Is there a way of applying the true displacement
There is no way to do that (at least currently) and unless your object covers a distance that would make adaptive subdivision useful (has parts that are far and others that are close), you should use a Subdivision Surface and a Displace modifier. If your object does cover a big distance and you want to have a decreasing amount of detail over the distance, the only workaround I know is dyntopo.


in sculpt mode, select the SculptDraw brush and set the strength to zero. 
enable Dyntopo in relative detail mode
from your camera's point of view, paint a stroke at each distance step. Don't paint a single stroke ! The detail is defined from where you click and stays this way until you release the click, so if you paint multiple strokes in multiple steps, it should give a very similar result to adaptive subdivision. However it may not be as easy to paint on for every object. I tried with a plane and it worked fine (I selected Subdivide Edges in Dyntopo to avoid deforming the sides).
If it's impossible to do from your camera's point of view because of the shape of your object you'll have to move around and tweak the detail size manually and maybe select the Constant Detail mode in Dyntopo instead.